Identification and utilization of sheep major fecundity genes offer opportunities for the increase in litter size, as well as the improvement of production efficiency in livestock industry. BMPR-IB gene belongs to the TGF-β superfamily, and is also considered as a regulator for sheep reproductive performance due to its involvement in the mammalian gametogenesis pathway. This study aimed to detect the variations of BMPR-IB gene in Hu sheep (N = 934) and to evaluate their effects on the litter size trait. qRT-PCR results showed that the mRNA expression level of BMPR-IB in kidney was the highest. And in the tissues of ovary and pituitary, the expression levels of prolific group were significantly higher than that of non-prolific group (p < 0.05). Through DNA sequencing and PCR-RFLP, three SNPs were identified in the genomic region of BMPR-IB gene; the individuals with CC in g.29362047T > C, AA in g.29427689G > A and GG in FecB had better fecundity characterization. Additionally, association analysis indicated that two diplotypes of Hap2/2 and Hap2/4 showed larger litter size. Overall, our results verified several useful markers which would contribute to further development of sheep breeding strategies.